1. Field of the Invention
The invention relates to a data transmission system for transmitting data between a rotating part and a stationary part, in particular between the rotating part and the stationary part of a computer tomograph, and also to a computer tomograph having a corresponding transmission system.
2. Description of the Relevant Art
With rotatable units such as radar installations or also computer tomographs, and also with linearly movable units such as crane and conveyor systems it is necessary to transmit electrical signals or energy between units that are movable relative to each other. For this, usually a conductor structure is provided in a first unit, and a suitable tap in a second unit. In the following explanations the term conductor structures refers to all conceivable forms of conductor structures which are suitable for conducting electrical signals. This also refers to the known contacting slide tracks or slip rings. Essential to transmission by means of rotary joints or linear “slide lines” which also may be designed to be non-contacting is a small distance of transmission between the units that are movable relative to each other. Thus a signal can be coupled-out optionally by electrical contact or without contact in a near field of the conductor structures.
A device for data transmission in computer tomographs is known from U.S. Pat. No. 6,433,631 B2. A strip line in a rotating part is supplied with a signal to be transmitted. On the stationary part a tap is provided which is guided along at a small distance of an order of magnitude of about 1 mm from the strip line. With computer tomographs the length of the strip line is of an order of magnitude of about 5 meters. Thus, with data transmission rates of a few tens of gigabits per second, signals having a bandwidth of several gigahertz must be passed through a conductor system having a length of about 5 meters. With this, and particularly at higher frequencies, considerable dielectric losses occur. The dielectric losses are determined by the material of the dielectric of the strip line. Materials having few dielectric losses are extremely expensive, and usually also difficult to machine.
A duobinary encoder is disclosed in U.S. Pat. No. 3,457,510. This consists of a digital logic followed by a band-pass filter.
A capacitive rotary joint having a band-pass characteristic is disclosed in EP 1 012 899 A. This is a band-pass filter of high order, having extremely steep filter flanks.
A duobinary pre-coder is disclosed in WO 2006/043268 A1.